Hubble makes 3D dark matter map

In article ,
wrote:

Yet another suggestion for dark matter, that comes to my mind, is dark
planetary systems, that is, essentially a star system before the star has
ignited. Is that possible or impossible by current theoretical knowledge?

Well, the planets are a bit of a red herring he the star completely
dominates the mass of a star system, so what you're asking is whether
protostars can be the dark matter. The answer is no for any number of
reasons.
First, protostars are observable, especially in the infrared, so we
have quite a good idea of how many there are. Second, a protostar
remains a protostar for only a limited time before becoming a star.
So the number of stars we see sets a good limit on the number of
protostars.

But before they even heat up, would they then be observable?

--
Hans Aberg

In article ,
Hans Aberg wrote:
In article ,
wrote:

Well, the planets are a bit of a red herring he the star completely
dominates the mass of a star system, so what you're asking is whether
protostars can be the dark matter. The answer is no for any number of
reasons.
First, protostars are observable, especially in the infrared, so we
have quite a good idea of how many there are. Second, a protostar
remains a protostar for only a limited time before becoming a star.
So the number of stars we see sets a good limit on the number of
protostars.

But before they even heat up, would they then be observable?

Yes, because they're great big clouds of gas. Depending on
temperature and composition, you see them in emission in the infrared
or radio, or in absorption in the visible.

Besides, if you're trying to make the dark matter of out objects like
this, then presumably they won't all be young and cold right now: some
will have heated up and become stars. We really do have an extremely
good idea of how many objects like this there are out there, and
they're not the dark matter.

-Ted

--
[E-mail me at , as opposed to .]

In article ,
wrote:

... protostars are observable, especially in the infrared, so we
have quite a good idea of how many there are. Second, a protostar
remains a protostar for only a limited time before becoming a star.
So the number of stars we see sets a good limit on the number of
protostars.

But before they even heat up, would they then be observable?

Yes, because they're great big clouds of gas. Depending on
temperature and composition, you see them in emission in the infrared
or radio, or in absorption in the visible.

Besides, if you're trying to make the dark matter of out objects like
this, then presumably they won't all be young and cold right now: some
will have heated up and become stars. We really do have an extremely
good idea of how many objects like this there are out there, and
they're not the dark matter.

Well, small, young, nearby*galaxies are very hard to observe, despite the
fact they are lit.

I thought that dark matter, whatever it may be,*would clump up because of
gravity.

--
Hans Aberg

In article ,
Hans Aberg wrote:

Well, small, young, nearby*galaxies are very hard to observe, despite the
fact they are lit.

I'm not sure what your point is. I though we were talking about the
dark matter in our Galaxy. If the dark matter were great big clumps
of gas, some of it would be right around here (within tens of light-years,
say). It's really not the same thing as looking for other galaxies
millions of light-years away.

If you're really serious about thinking about what dark matter candidates
are viable, I think you should probably read up quite a bit on what
we know about the distribution of visible matter in our Galaxy.

I thought that dark matter, whatever it may be,*would clump up because of
gravity.

True. Again, I'm not sure what your point is.

-Ted

--
[E-mail me at , as opposed to .]

In article ,
wrote:

Well, small, young, nearby*galaxies are very hard to observe, despite the
fact they are lit.

I'm not sure what your point is.* I though we were talking about the
dark matter in our Galaxy.*

Both, if you look at the map in the beginning of this thread. But I guess
this*sub-discussion focuses mainly on the dark matter in our discussion.
What reason is there to believe that dark matter in our*galaxy is
any*different from the one between the galaxies?

If the dark matter were great big clumps
of gas, some of it would be right around here (within tens of light-years,
say).* It's really not the same thing as looking for other galaxies
millions of light-years away.

If you're really serious about thinking about what dark matter candidates
are viable, I think you should probably read up quite a bit on what
we know about the distribution of visible matter in our Galaxy.

I don't see the connection here, nor what you have in your mind.

I thought that dark matter, whatever it may be,*would clump up because of
gravity.

True.* Again, I'm not sure what your point is.

The point is that if dark matter is clumped up, wast regions might
be*sufficiently empty that it might be difficult to observe. You can only
see clumped up dark matter by observing the light that passes through it.

I am not proposing this as a theory: rather you say this surely cannot be
so, so I want to know your reasoning.

Regardless whether it is clumped up or not, it is hard to observe. If it
is clumped up, the*regions must be*sufficiently narrow to be hard to
observe with todays telescopes. It means that it cannot consist of wast,
dense clouds. Assume, just as a thought experiment, that it consists
mainly of small black holes. Would it then be observable?

--
Hans Aberg

Thus spake Hans Aberg
Assume, just as a thought experiment, that it consists mainly of small
black holes. Would it then be observable?

I believe this would be potentially observable with microlensing, and
that the prospect has been eliminated. Typically, I can't remember where
I read this, so no references, sorry. In fact, apart from the expected
amount of conventional dark matter, I believe that we can eliminate any
conventional form of matter as candidates for cold dark matter. For
example, matter which simply obeys conventional gravity would have a
similar mass distribution to that observed for visible matter in
galaxies. That is not true of galactic haloes, so Cold Dark Matter has
to be subject to additional, and unknown forces.


Regards

--
Charles Francis
substitute charles for NotI to email

In article , Oh No
wrote:

Assume, just as a thought experiment, that it consists mainly of small
black holes. Would it then be observable?

I believe this would be potentially observable with microlensing, ...

Perhaps. In addition, star orbits in the galaxy would be effected.

...and
that the prospect has been eliminated.

But I would not be so sure about this point.

Typically, I can't remember where
I read this, so no references, sorry. In fact, apart from the expected
amount of conventional dark matter, I believe that we can eliminate any
conventional form of matter as candidates for cold dark matter. For
example, matter which simply obeys conventional gravity would have a
similar mass distribution to that observed for visible matter in
galaxies.

Why would this be the case? - The dark matter map in the beginning of this
thread shows that there is dark matter also in some places where there are
no galaxies.

--
Hans Aberg

In article ,
Hans Aberg wrote:
In article ,
wrote:

Both, if you look at the map in the beginning of this thread. But I guess
this*sub-discussion focuses mainly on the dark matter in our discussion.
What reason is there to believe that dark matter in our*galaxy is
any*different from the one between the galaxies?

None. It's probably the same, or at least largely the same. If by
dark matter we mean stuff that we don't see directly but whose
gravitational effects we can measure, then there appear to be (at
least) two constituents: "baryonic dark matter" (stuff made of
ordinary atoms) and "nonbaryonic dark matter" (mysterious other
stuff). There's probably some of both everywhere, but the relative
amounts of the two are likely to be different in the Galaxy and in
intergalactic space.

If the dark matter were great big clumps
of gas, some of it would be right around here (within tens of light-years,
say).* It's really not the same thing as looking for other galaxies
millions of light-years away.

If you're really serious about thinking about what dark matter candidates
are viable, I think you should probably read up quite a bit on what
we know about the distribution of visible matter in our Galaxy.

I don't see the connection here, nor what you have in your mind.

Likewise!

I thought that you were interested in the question of what candidates
for dark matter are viable. One of the main ways of ruling out a dark
matter candidate is to realize that it wouldn't be "dark" -- that is,
that we'd be able to see it. So if you want to think seriously about
dark matter, you've really got to learn a bit about non-dark matter.

For example, I understood you to be asking a question roughly like
this: Is it possible that the dark matter in our Galaxy is composed of
protostars (with or without their associated planetary systems)? I
was trying to explain why the answer to that is no. The reason is
that objects like that would be visible in a variety of ways, so they
can't be the (by definition unseen) dark matter.

If that's not what you were asking, then never mind.

I thought that dark matter, whatever it may be,*would clump up because of
gravity.

True.* Again, I'm not sure what your point is.

The point is that if dark matter is clumped up, wast regions might
be*sufficiently empty that it might be difficult to observe. You can only
see clumped up dark matter by observing the light that passes through it.

OK so far. Now let's talk about what this clumped-up matter is made
of. I thought that we were considering the possibility that it was
stuff with a lot of hydrogen gas in it. We know a lot about what
stuff with a lot of hydrogen gas in it looks like when it's clumped up
on various size scales: if it's sufficiently densely clumped, we call
it "stars" or "brown dwarfs"; if it's somewhat less clumpy, we call it
"protostars," "molecular clouds," "gaseous nebulae," or a variety of
other things depending on context. All of those things are observable
in a variety of different ways. As a result, we have good estimates
of how much of them there are in our Galaxy, and it's not enough to be
the Galactic dark matter.

Regardless whether it is clumped up or not, it is hard to observe.

Hard, maybe -- I'll let the people who do it give opinions on that --
but not impossible. On the contrary, observations of clumps of gas
is done all the time. Honest, a huge amount is known about how
the gas in our Galaxy is distributed.

If it
is clumped up, the*regions must be*sufficiently narrow to be hard to
observe with todays telescopes. It means that it cannot consist of wast,
dense clouds. Assume, just as a thought experiment, that it consists
mainly of small black holes. Would it then be observable?

There probably is some parameter space for black holes as candidates
for the Galactic dark matter. There are constraints on how big they
can be to have avoided detection by microlensing surveys, but I'd
guess that if you choose the right sizes you might be able to "hide"
them. (There would then be all sorts of interesting puzzles about how
they formed in the first place.)

-Ted

--
[E-mail me at , as opposed to .]

In article ,
Hans Aberg wrote:
In article , Oh No
wrote:

Assume, just as a thought experiment, that it consists mainly of small
black holes. Would it then be observable?

I believe this would be potentially observable with microlensing, ...

Perhaps. In addition, star orbits in the galaxy would be effected.

Depends what you mean by "small". I'd guess -- although I'm not sure
-- that the best way to make a viable model in which the Galactic dark
matter consisted of black holes would be to make them much, much
smaller than a solar mass. That would, if I'm not mistaken, make the
microlensing signal hard to detect.

-Ted

--
[E-mail me at , as opposed to .]

On Jan 30, 11:12 am, wrote:

-- that the best way to make a viable model in which the Galactic dark
matter consisted of black holes would be to make them much, much
smaller than a solar mass. That would, if I'm not mistaken, make the
microlensing signal hard to detect.


1. Several microlensing groups have independently observed
microlensing events with estimated masses for the lensing objects in
the 0.1 to 0.6 solar mass range.

2. The numbers of lensing objects, found in the halo, disk and bulge,
tend to be a factor of 3 to 5 times higher than any known conventional
objects.

3. The estimated abundances for these objects ranges from roughly 10
to 30 percent of the estimated abundance of galactic dark matter. That
means that there is observational evidence for a very large number of
these mystery objects.

4. Similar results have been observed for the Andromeda galaxy (M31).

5. These well-documented scientific facts are discussed in more detail
in the thread entitled "Critical Test of the ... Paradigms" at this
newsgroup.


Reasonable questions:

A. If these are not black holes, what are they? Chopped liver?

B. Why, in the name of all we scientists are supposed to hold dear, do
intelligent scientists who are fully aware of these microlensing
results act like the observational results do not exist?

C. When there is scientific evidence for actual stellar-mass dark
matter objects, why do scientists focus all their attention on
completely hypothetical "Cold Dark Matter" which has been a dependable
"no show" in 100s of experiments run over the last few decades?

Robert L. Oldershaw